Two new cysteine endopeptidases obtained from the latex of Araujia hortorum fruits

Two new endopeptidases were purified to homogeneity from the latex of Arauj ia hortorum fruits by a simple purification procedure involving ultracentri fugation and ion exchange chromatography. Molecular weights of araujiain h II and araujiain h III were 23,718 and 23546 (mass spectrometry), respactiv ely. The isoelectric point of araujiain h II was 8.9, whereas araujiain h I II had a pI higher than 9.3. Maximum proteolytic activity on caseine was re ached at pH 8.0-9.0 for both endopeptidases, which were irreversibly inhibi ted by iodoacetate and E-64, suggesting they belong to the cysteine proteas e family. Esterolytic activity was determined on N-alpha -CBZ-amino acid-be ta -nitrophenyl esters, and the highest k(cat)/K-m values for the both enzy mes were obtained with the glutamine derivative. The N-terminal sequences o f araujiain h II and araujiain h III showed a high degree of homology with other plant cysteine endopeptidases.